Method and apparatus for efficiently coordinating data center cooling units

ABSTRACT

Methods and systems for controlling environmental maintenance modules (e.g. HVAC units) using sensors are provided. Values measured by the sensors can be used to determine a change in operation levels of the modules to keep the sensor values within a desired range. For example, a stopped module can be increased or started for more cooling when a sensor temperature is too hot. The module predicted to have the greatest effect on the temperature of hot sensor can be started. As another example, a module can be stopped (or otherwise have an operation level decreased), if the sensor temperatures are within range, and the decrease in operation level is predicted not to cause an out-of-range condition.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application claims priority from and is a Divisional of U.S.Non-Provisional application Ser. No. 12/860,820, by C. Federspiel etal., entitled “Method and Apparatus for Efficiently Coordinating DataCenter Cooling Units” filed Aug. 20, 2010, which claims the benefit ofU.S. Provisional Application No. 61/235,759 by C. Federspiel et al.,entitled “Method And Apparatus For Coordinated Starting And Stopping OfDatacenter Cooling Units” filed Aug. 21, 2009, the entire contents ofwhich are herein incorporated by reference for all purposes. The presentapplication is also related to U.S. Non-Provisional application Ser. No.12/396,944 by C. Federspiel, entitled “Method and Apparatus forCoordinating the Control of HVAC Units” (Attorney Docket No.027332-000110US) filed Mar. 3, 2009, the entire contents of which areherein incorporated by reference for all purposes.

BACKGROUND

The present invention generally relates to environmental controlsystems, such as heating, ventilation, and air conditioning (HVAC)systems, which can be used to control the temperature and humidity ofcommon spaces, e.g., as can exist in data centers containing servercomputers. More, specifically the present invention can relate toefficiently maintaining certain environmental conditions by increasingor decreasing an operation level (e.g. starting and stopping) ofrespective units (modules) of an environmental control system.

Modern datacenters use HVAC systems to control indoor temperature,humidity, and other variables. It is common to have many HVAC unitsdeployed throughout a data center. They are often floor-standing units,but may be wall-mounted, rack-mounted, or ceiling-mounted. The HVACunits also often provide cooled air either to a raised-floor plenum, toa network of air ducts, or to the open air of the data center. The datacenter itself, or a large section of a large data center, typically hasan open-plan construction, i.e. no permanent partitions separating theair in one part of the data center from the air in another part. Thus,in many cases, these data centers have a common space istemperature-controlled and humidity-controlled by multiple HVAC units.

HVAC units for data centers are typically operated with decentralized,stand-alone controls. It is common for each unit to operate in anattempt to control the temperature and humidity of the air entering theunit from the data center. For example, an HVAC unit may contain asensor that determines the temperature and humidity of the air enteringthe unit. Based on the measurements of this sensor, the controls of thatHVAC will alter operation of the unit in an attempt to change thetemperature and humidity of the air entering the unit to align with theset points for that unit.

For reliability, most data centers are designed with an excess number ofHVAC units. Since the open-plan construction allows free flow of airthroughout the data center, the operation of one unit can be coupled tothe operation of another unit. The excess units and the fact that theydeliver air to substantially overlapping areas provides a redundancy,which ensures that if a single unit fails, the data center equipment(servers, routers, etc.) will still have adequate cooling.

As mentioned above, the standard operating procedure for the HVAC unitsis to control the return air temperature into each HVAC unit. Suchoperation is not aware of the temperature of the air entering theservers and other computing equipment in the data center. Since thisinformation is not available to the HVAC unit controls or to the datacenter operators, the extra HVAC units are typically run at all times,to ensure that the servers are kept cool. However, such precautionarymeasures waste energy.

While it is possible to manually turn off redundant HVAC units to saveenergy, doing so poses a risk of overheating that equipment. Also, somedata centers have variable loads, in which case it may be necessary tostop and start several units throughout the day. Furthermore, thecomplex and tightly coupled airflow patterns in a data center make itdifficult for an operator to know which HVAC unit will be the mosteffective to restart should a need be identified.

Therefore, it is desirable to provide methods and systems that canautomatically reduce operation levels of redundant HVAC units (e.g.without triggering elevated temperatures), and that can automaticallyincrease operation levels when necessary and in an efficient manner.

BRIEF SUMMARY

Embodiments of the present invention can provide systems and methods forcontrolling environmental maintenance modules (e.g. HVAC units) usingsensors. In various embodiments, a system can heat and/or cool anenvironment. The sensors can measure temperatures at various locationswithin the environment, and this temperature feedback can be used tochange operation levels of the modules to keep the temperatures within adesired range.

For example, stopped modules can be started (or otherwise have anoperation level increased) for cooling when a sensor temperature is toohot. In one embodiment, the module for starting is one that is predictedto have the greatest or at least a sufficiently large effect on thetemperature of a hot sensor. As another example, a module can be stopped(or otherwise have an operation level decreased), if the sensortemperatures are within range, and the decrease in operation level ispredicted not to cause an out-of-range condition. In one embodiment, atransfer matrix is used to perform the above predictions. In one aspect,the transfer matrix can provide a relation between a change in operationlevel of a module and resulting temperature differences for each sensorin the system.

According to an embodiment, a method of controlling an environmentalmaintenance system is provided. The system includes a plurality ofenvironmental maintenance modules and a plurality of sensors, where thesensors measure a value of a physical condition of an environment. Asensor S_(indx) is identified whose sensor value is measured to beoutside of a range. For each of at least a portion of the modules, apredicted change value is determined.

Each predicted change value predicts an extent that changing anoperation level of the respective module changes the sensor valuemeasured by the identified sensor S_(indx). A module is selected basedon the predicted change values. The operation level of the selectedmodule is changed to effectuate a change of the sensor value of sensorS_(indx).

According to another embodiment, a method of controlling anenvironmental maintenance system is provided. The system includes aplurality of environmental maintenance modules currently running and aplurality of sensors that measure a value of a physical condition of anenvironment. At least one of the plurality of the modules currentlyrunning is analyzed. The system estimates sensor values of the sensorsthat would result if an operation level of the module were decreased byat least a predetermined amount. A first set of the modules currentlyrunning that have none of the estimated sensor values outside of a firstrange is determined. An operation level of at least one module of thefirst set is decreased in response predicting that an out-of-rangecondition will not occur (e.g. that none of the estimated sensor valuesare outside of the first range).

According to another embodiment, a method of initializing anenvironmental maintenance system is provided. Each module includes oneor more actuators. A first sensor value Y1 is received for each of thesensors. An operation level of at least two actuators of the modules ischanged at a same time. After the change in operation levels, a secondsensor value Y2 is received for each sensor. A difference between thefirst sensor value Y1 and the second sensor value Y2 is calculated. Atleast a portion of matrix elements of a transfer matrix TM determinedbased on the differences. The transfer matrix can have dimensions of anumber of actuators by a number of sensors. The portion of TM includesmatrix elements associated with the at least two actuators. Determininga matrix element for sensor S and actuator P includes: determining afirst ratio having a numerator including the difference for sensor S andhaving a denominator including the change in operation level foractuator P; and combining the first ratio with at least one other ratio.The at least one other ratio is determined from a previous change of theoperation level of actuator P that resulted in a previous difference inthe sensor values for sensor S.

According to another embodiment, a method of initializing anenvironmental maintenance system is provided. At least one processordetermines a transfer matrix TM. For each one of the modules, a firstsensor value Y1 is received for each of the sensors. Each first sensorvalue is received when the respective module has a first operationlevel. Stopping or starting the respective module, and then a secondsensor value Y2 is received for each sensor. A difference is calculatedbetween the first sensor value Y1 and the second sensor value Y2. A TMmatrix element is calculated using the difference, thereby obtaining atransfer matrix TM that provides a relation between starting and/orstopping a module and resulting changes in the sensor values for eachsensor.

Other embodiments of the invention are directed to systems, devices, andcomputer readable media associated with methods described herein.

As used herein, an environmental maintenance module may be an HVAC unit,a computer room air conditioner (CRAC) unit, or any device that receivescontrol signals and provides an output that is designed to achieve ormaintain an environmental condition in a specific area. A use herein, anoperation level can be a value of an operational parameter (input oroutput) that measures how much effort is being expended by a module toperform an operation, such as heating of cooling. Operation levels of amodule can include stopped, operating at full power, percentages ofinput power levels, percentages or values for operation of a particulardevice within the module (e.g. a fan speed, temperature setpoint,humidity setpoint, or valve position), and percentages or values of theoutput heating or cooling power of the output air stream, e.g., ascompared to a reference level.

A better understanding of the nature and advantages of the presentinvention may be gained with reference to the following detaileddescription and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a data center according to an embodiment of thepresent invention.

FIG. 2 is a plan view of an open-plan building conditioned by unitaryrooftop units according to an embodiment of the present invention.

FIG. 3 is a schematic diagram of a computer room air handling unit 300according to an embodiment of the present invention.

FIG. 4 is a block diagram of a control system 400 for providingmaintenance of environmental conditions within a building according toan embodiment of the present invention.

FIG. 5 is a flow diagram illustrating a method 500 of initializing anenvironmental maintenance system including a plurality of modules (e.g.CRAC units) and sensors according to an embodiment of the presentinvention.

FIG. 6 is a flow diagram illustrating a method 600 of controlling anenvironmental maintenance system to maintain sensor values within adesired range with high efficiency according to an embodiment of thepresent invention.

FIG. 7 is a flow diagram illustrating a method 700 of controlling anenvironmental maintenance system by decreasing operation of actuatorsaccording to an embodiment of the present invention.

FIG. 8 is a flow diagram illustrating a method 800 of controlling anenvironmental maintenance system including a plurality of modules andsensors by stopping modules according to an embodiment of the presentinvention.

FIG. 9 is a flow diagram illustrating a method 900 of controlling anenvironmental maintenance system by starting and stopping modulesincluding a plurality of modules and sensors according to an embodimentof the present invention.

FIG. 10 is a plot showing an equation for updating the trace of thecovariance matrix based on a size of a prediction error.

FIG. 11 shows a block diagram of an exemplary computer apparatus usablewith system and methods according to embodiments of the presentinvention.

DETAILED DESCRIPTION

To ensure that an environment (e.g. a data center) is sufficiently coolor warm, standard operating procedure is to operate extra HVAC units (orother environmental maintenance modules) beyond what is marginallyrequired. However, such precautionary measures waste energy. Variousembodiments can analyze sensors throughout the environment (e.g.,sensors across modules or at locations outside of modules) to determinewhether the operation levels of specific modules can be safely reducedand whether increased operation is required (e.g. due to an out-of-rangemeasurement), including which module is optimal for bringing the sensorback in range. Such embodiments can provide stable environments whilereducing energy consumption. A transfer matrix can be used in performingthe above determinations. In one aspect, the transfer matrix can providea relation between a change in operation level of a module and resultingtemperature differences for each sensor in the system.

Another problem with running many redundant HVAC units, particularlywhen they deliver air to an underfloor plenum is that the discharge airtemperature from the HVAC units can be higher than if fewer HVAC unitswere used. The discharge air temperature can be higher because, withmore HVAC units being used, the temperature can be higher while stillextracting the same amount of heat from the servers. In other words, agreater airflow (with the higher number of HVAC units) for extractingheat from the servers means that the discharge temperatures from theHVAC units can be higher. As a result, a concrete slab floor or a raisedfloor will not be as cool, which diminish disaster recoverycapabilities. For example, having a cool floor increases the timeavailable to recover from a cooling failure (e.g. when power is cut offfor an entire building) because the slab and floor acts as cool storagemedia (heat sink). A colder temperature of a floor can keep the serverscooler when the HVAC units are not pushing out cool air, e.g., due topower being cut off.

I. System Overview

FIG. 1 shows a floor plan of a data center according to an embodiment ofthe present invention. Perimeter wall 1 may be the perimeter wall of adata center or the perimeter wall of a commercial building such as aretail store. A data center includes a plurality of HVAC units 2 (orother environmental maintenance modules), a plurality of environmentalsensors 3, and a plurality of server racks 4. As shown, the HVAC unitsare computer room air conditioner (CRAC) units.

In one embodiment, HVAC units 2 are unitary equipment that provideairflow to the data center to cool servers in server racks 4. In oneaspect, HVAC units 2 can cool, heat, humidify, or dehumidify air thatpasses through them. Environmental sensors 3 are devices that measureenvironmental parameters, such as temperature or humidity. Environmentalsensors 3 can transmit measurements (also called readings) by any means,such as by wired or wireless communication means (e.g., Modbus, BACnet,Wi-Fi, WiMAX, ZigBee, or any other applicable protocol). The HVAC units2 (and other modules mentioned herein) can be controlled by a computersystem with one or more processors to provide specified conditionswithin the data center.

FIG. 2 is a plan view of an open-plan building conditioned by unitaryrooftop units according to an embodiment of the present invention. Inthis example, the HVAC units are roof top units (RTU) 2. Perimeter wall5 is an outside or inside wall of a commercial building such as a retailstore or space within such a building or store. As depicted, a wiredcommunication occurs between the RTU 2 and sensors 3 near thatparticular RTU, but wireless communications may also be used.Merchandise racks 6 and a store checkout counter 7 are also shown.

FIG. 3 is a schematic diagram of a computer room air handling unit 300according to an embodiment of the present invention. Computer room airhandling unit 300 is an example of an environmental maintenance module.As shown, computer room air handling unit 300 has a cooling coil 310,which may contain chilled water modulated by a chilled water valve 320.The computer room air handling unit 300 also has a reheat coil 330 (e.g.an electric coil) and a humidifier 340 (e.g. an infrared humidifier).

In one embodiment, fan 350 is a centrifugal fan driven by an A/Cinduction motor. The induction motor may have a variable speed(frequency) drive VSD 355 for changing its speed. A wireless sensor 360measures return air temperature, a wireless sensor 370 measuresdischarge air temperature, and a wireless control 380 to control the VSD355. The discharge air temperature sensor 370 and return air temperaturesensors 360 may be probes tethered to the wireless control 380 ratherthan separate wireless sensors.

In one embodiment of operation, the wireless sensors 360,370 sendreadings over the radio to a wireless network gateway, which passes thesignals to a control computer, e.g. which contains supervisorycontroller 15 of FIG. 4. Supervisory control 15 may be a computer systemitself. The control computer can send actuation commands to the wirelessgateway, which relays the commands to the wireless control 380, whichchanges the speed of the variable speed drive 355.

FIG. 4 is a block diagram of a control system 400 for providingmaintenance of environmental conditions within a building according toan embodiment of the present invention. In this example, control system400 comprises HVAC units 2 (such as unit 300), a plurality ofenvironmental sensors 3, and a supervisory controller 15, which includesone or more processors 10 for performing calculations. The HVAC units 2include final control elements (also called actuators), e.g., for fans,valves, or temperature elements, which may be used in maintaining theenvironment of a space. Inputs and outputs of the actuators maycorrespond to operation levels of a module, as mentioned herein. In oneaspect, supervisory controller 15 can control the final control elementsto have operation levels (including on and off, and variations inbetween) to provide stable environmental conditions using a reduced orminimal amount of energy.

Modules (HVAC Units)

In some embodiments, supervisory controller 15 can coordinate theoperation of multiple HVAC units 2 by computing commands to inputs 12 ofeach HVAC unit 2. The commands are computed based on the environmentalsensor readings from the sensors 3. The inputs 12 may correspond to avariety of different HVAC units 2 and/or devices or circuits within theHVAC units 2.

In one embodiment, input 1 of HVAC unit 1 may correspond to theoperational parameter of one actuator (e.g. a fan, temperature setpoint,humidity setpoint, or valve position), and the input 2 of HVAC unit 1may correspond to a different actuator of the same HVAC unit 1. Theoperational parameter may have different operation values (levels), eachresulting in a consumption of different amounts of energy. In anotherembodiment, some of the HVAC units 2 have only one input for control ofan operation level.

In other embodiments, a setpoint for the temperature of an HVAC unit 2can also be provided from supervisory controller 15. For example, asetpoint may be the desired temperature of the air discharged by theHVAC unit 2, or the desired temperature of the air returning to theunit. Other inputs could be the setpoint for the humidity (or thehumidifier command), or a command to a variable frequency drive (VFD).

In one embodiment, each HVAC unit has the same number of inputs, eachcorresponding to one actuator of that HVAC unit. In another embodiment,different HVAC units may have a different number of actuators. In suchan embodiment, the number of sensors may be the same regardless of thetotal number of actuators. In part, a reason the number of sensors maystay the same is because each sensor may affect each actuator, and viceversa. For example, a temperature actuator (e.g. cooling valve) canaffect the humidity as may happen when condensate forms on the coolingcoil if the environment is cold enough. Likewise, humidity actuators(e.g. infrared humidifiers and evaporative cooling valves) affect thetemperature, as may happen when infrared humidifiers raise humidity orevaporative coolers raise humidity.

Sensors

Environmental sensors 3 can measure a value of a physical condition ofan environment, such as temperature, humidity, and pressure.Environmental sensors 3 can send their readings back to supervisorycontroller 15, e.g., by wired or wireless communication means (such asModbus, BACnet, Wi-Fi, WiMAX, ZigBee, or any other applicable protocol).Examples of sensors include temperature sensors, humidity sensors, andpressure sensors. A single sensor may be able to measure multipleenvironmental condition, e.g., all three of the above conditions. Theenvironmental sensors 3 may be positioned randomly or according to aregular pattern. The environmental sensors 3 may also be organized viaclusters of sensors or individually placed.

In some embodiments, supervisory controller 15 causes temperature sensorreadings F to be within a temperature range R, e.g., as specified by anassociated set of reference values 8. The range can simply be less thana certain temperature (e.g. less than 78 degrees Fahrenheit). The rangecan also be specified by two temperatures. Such a temperature range canbe as small or as large as is desired. Such ranges can also be appliedto heating. Certain embodiments can attempt to maintain a specifiedtemperature range for each temperature (all of which may be different orbe the same for each temperature sensor) while using a minimal amount ofenergy.

In one embodiment, supervisory controller 15 internally stores the setof desired reference values 8 for each environmental sensor, e.g. inflash memory, cache, or other suitable memory. In other embodiments, thereference values 8 may be stored externally, e.g. in a disk drive oroptical drive. In operation, supervisory controller 15 adjusts operationlevels of HVAC units 2 to keep the values from environmental sensors 3with the specified range using a minimal amount of energy (e.g. byhaving the fewest possible modules running without exceeding thetemperature range).

Inputs To HVACs

In one embodiment, supervisory controller 15 computes commands that areprovided to inputs 12 and are used directly for final control elements(e.g. actuators) in HVAC units 2. These commands sent to the inputs 12may be provided, e.g., by wired or wireless communication means. Thesecommands may start, stop, or change any number of operation levels ofthe HVAC units 2.

In another embodiment, supervisory controller 15 computes commands tothe inputs 12 that are used by a local digital controller (e.g. havingmicroprocessor-based controls) in an HVAC unit 2. In one aspect, eachinput to the local digital controller of a unit corresponds to anactuator of the unit. The local digital controller can then determinethe final commands sent to the final control elements. For example, thelocal digital controller may convert a digital signal to an analogsignal for the actuator, or convert a protocol of the signal to beusable by an actuator. The local digital controller may also operate tomaintain an actuator at a particular setting through a local controlloop. Thus, supervisory controller 15 may command the setpoints of localcontrol loops in the local digital controllers rather than directlycommanding the final control elements.

Status Indicators

In one embodiment, supervisory controller 15 has means of receivingstatus indicators 13 from the environmental sensors 3 and/or the HVACunits 2. In one aspect, the status indicators 13 can provide informationas to whether an HVAC unit 2 or a sensor 3 is presently operational. Inanother aspect, the status indicators 13 can provide settings of theHVAC units, such as return air temperature, discharge temperature,portion (e.g. percent) of the capacity of the unit that is being used(which is an example of an operation level), and how much a chilledwater valve (e.g. 320) is open. The status indicators 13 are shownseparated from the HVAC units 2 and sensors 3 for illustrative purposes,and may actually be received from the HVAC unit 2 or sensor 3themselves.

In one embodiment, the status indicators 13 for the HVAC units 2 may beobtained from local digital controllers of the HVAC units 2. These localdigital controllers can be queried by supervisory controller 15 todetermine if the local digital controllers or the HVAC units 2 are “on”or “off”. If a unit is “off”, then the status indicator 13 for thatunit's actuators could be a certain value, e.g., zero.

In another example, the environmental sensors 3 have some well-definedand easily detected failure modes. In one aspect, one failure mode is an“unreachable”, which means that a gateway, e.g. a network interface ofthe supervisory controller 15, cannot communicate with the sensor.Another failure mode is an out-of-range voltage (either 0 volts or 1.5volts), where 0 volts implies that the sensor probe has a short circuitand 1.5 volts indicates that the sensor probe has an open circuit or ismissing. Any of these failures may result in a status indicator of zerofor that sensor.

During operation of the system 400, not all of the HVAC units 2 may berunning in an attempt to conserver energy. However, system 400 maydetect a hotspot (e.g. a temperature sensor 3 above a referencetemperature) or other event where more cooling (or heating in otherembodiments) is desired, and then determine which module should have itsoperation level increased (e.g. if the module should be turned on).System 400 may also determine when it is acceptable to decrease anoperation level (e.g. turn off) of an HVAC unit 2, along with which HVACunits 2 are acceptable for decreasing without causing sensor readings togo out of range. As part of these determinations, a transfer functionmatrix (TM) and a load matrix (LOAD) may be used.

II. Initializing Transfer Function and Load Matrices

The transfer function matrix (TM) is a measure of the effect ofincreasing (and potentially equivalently decreasing) an environmentalmaintenance module on an environmental sensor. The matrix can providethe effect for every sensor in the system, or just a portion of thesensors. In one aspect, the number of rows J of TM can equal the numberof environmental sensors (also called cold aisle sensors for embodimentsusing CRAC units), and the number of columns can equal the number ofenvironmental maintenance modules. Thus, in one embodiment, there isonly one column for each module. In such an embodiment, there would beonly one measure of the energy consumption of a module, i.e., oneparameter for which an operation level is determined. In anotherembodiment, there may be more than one row for a module, and thus therecan be more than one parameter, each providing a measurement of anoperation level of the module. Note that the rows and columns may beswitched. Also, the term “matrix” may be any indexable array of values.

As described herein, an operation level can be an input or an outputvalue. For example, an input command (e.g. a voltage or digital value)of no power can be an operation level of 0, and an input of full powercan be an operation level of 100% or some maximum value. The operationlevel can also be an input value for a particular actuator, e.g., a fanspeed, temperature setpoint, humidity setpoint, or valve position, or anoutput measurement of the positions of such actuators. In anotherembodiment, the operation level can also be an output level, e.g., alevel of cooling or heating provided. This output level can be apercentage of the actual flow relative to a designed value, which can beexceed thereby providing a percentage of greater than 100%. When theparameter is an output value, there can be one or more input commandvariables used to change the output parameter.

FIG. 5 is a flow diagram illustrating a method 500 of initializing anenvironmental maintenance system including a plurality of modules (e.g.CRAC units) and sensors according to an embodiment of the presentinvention. In describing the method, reference will be made to FIG. 4.The initialization involves the creation of the transfer matrix TM. Inone embodiment, the columns of TM are initialized by increasing and/ordecreasing operation levels of the modules (e.g. starting and stopping),and taking a difference between temperatures before and after the changein an operation level. In one embodiment, the modules are decreased andincreased sequentially (i.e. one at a time). In other embodiments, thecolumns of TM are initialized by changing the operation levels ofmultiple modules at a time.

In step 510, a first sensor value Y1 (e.g. temperature, humidity, orpressure) is received (e.g., at controller 15) for each of the sensors(e.g. from sensors 3). The first sensor value Y1 may be activelymeasured by a computer (e.g. controller 15) as a result of a measurementcommand, or passively obtained through a port able to receivetransmitted messages. The first sensor temperature Y1 for a specificsensor J may be written as Y1_(J). The first sensor values Y1_(J) may beobtained once or may be obtained multiple times. For example, the firstvalues Y1 may be obtained before the operation level of any module ischanged, or may be obtained each time before the operational level of aparticular module is changed.

In addition to the first sensor values Y1, other values may be recorded,such as an operation level of one or more operational parameters of amodule. Examples of operational parameters input settings and measuredoutput values, such as return temperatures (e.g. from sensors 360 inFIG. 3), discharge temperatures (e.g. from sensors 370), and flow rates(e.g., design flow rate times VFD percent command if the module has aVFD) may be measured and stored, e.g., in a memory communicably coupledwith controller 15.

In step 520, one or more operation levels of one or more modules arechanged. In one embodiment, all of the operation levels of a module arechanged, which may be just one level. In another embodiment, only someof the operation levels of a module are changed. The operation levelsnot changed may be changed at another time, or may not be included inthe calculation of the transfer matrix. In various embodiments,operation levels from multiple modules may be changed at the same time.

The amount of change in the operation levels may vary or may beequivalent in some manner. For example, each operational parameter thatis changed can be changed by the same percentage (e.g. 100%, 50%, 25%,etc.). In one implementation, a 100% is measured against a designedmaximum value for the parameter (e.g. 100% of the designed maximum airflow). It is possible to achieve an airflow greater than the designedair flow, and thus the percentage could be greater than 100%.

To determine the exact amount of change achieved for the operation levelof a particular parameter, a measurement may be made of the parameterafter a change command has been delivered. If the operational parameteris an output value, the new operation level may not be known directlyfrom the change command. For instance, the change command may be toincrease an airflow; and there may be some calibrated settings to knowgenerally what airflow corresponds to the command, but the actual valuefor the airflow may be obtained more accurately by measurement. Also,some parameters may not be known at all except by measurement of anoutput value. In other embodiments, the change in operational level maybe automatically known (e.g., if the change is to turn off, particularlyif there is only on and off).

In step 530, a second sensor value Y2 is received for each one of thesensors. In one embodiment, a timer (e.g., with a web-configurableperiod) is started after the operation level of the module is changed.As a default, the period may be 15 minutes. In one embodiment, thesecond values Y2 are measured after the end of the timer. In anotherembodiment, the values are continually measured after the change commandhas been given, and the second sensor value Y2 is stored after themeasured values come to a quasi-steady state condition. For example, thechanges outputs of the sensors may have a certain rate of change afterthe perturbation. Once the rate of change decreases below a threshold,then a quasi-steady state condition may be determined. Absolute valuesfor a threshold of changes in the outputs of the sensors is anotherexample

In step 540, a difference between each corresponding first sensortemperate Y2 and second sensor values Y2 is calculated (e.g. byprocessor 10). Thus, if there are N sensors being used, then there are Nrespective values of Y2_(J)−Y1_(J) for each operational parameter thatwas changed, where J runs from 1 to N. This difference may be positiveor negative. Typically for cooling, if the change is an increase inoperation level, then the temperatures (the sensor values of interestfor cooling) decrease and each Y2_(J)−Y1_(J) is negative. Also typicalfor cooling, if the change is a decrease in operation level, then thetemperatures increase and each Y2_(J)-Y1_(J) is positive. However, theserelations do not always hold true. For example, if the returntemperature of a module is at or below a desired discharge temperature,the module may turn off its cooling capacity. Thus, the module would notprovide cooling, but actually provide heating since the air would stillbe blown by a fan, which causes some heat to be imparted to the air.Thus, some transfer matrix elements can have opposite sign of others,which is counterintuitive.

In step 550, a TM matrix element is calculated, for each sensor, usingthe corresponding difference. For example, processor 10 may calculatethe NxK matrix elements, where N is the number of sensors and K is thenumber of operational parameters changed. In one embodiment, if oneoperational parameter is changed at a time, then a single column can beupdated at a time using a formula for each matrix element. In anotherembodiment, if more than one operational parameter is changed at a time,then multiple columns are updated at a time, with a combined formula(e.g. recursive least squares) being used to update the matrix elements.

In step 560, it is determined whether any more operational parametershave not been changed yet. If there are, then method 500 may repeat. Inone embodiment, assume that the first iteration of method 500 decreasedjust one operational parameter P₁. In the next iteration, step 520 caninclude increasing the level of parameter P₁ to have an operation levelof that before the last iteration, and step 520 can include decreasing alevel of parameter P₂. Thus, one operation level is changed on the firstiteration and two operational levels are changed on the seconditeration. Other embodiments can have multiple operation levelsdecreasing and multiple increasing at every iteration. Such embodimentscan use a recursive least squares method to determine the matrixelements, as is described below.

In one embodiment, this determination of whether any more operationlevels need to be changed is equivalent to whether any more columns ofTM need to be initialized. In an embodiment where there is one operationlevel for a module and the operation level options are on or off, thenthe determination is whether to start or stop a module. In such anembodiment, if there are more modules that need to be stopped, thestopped modules may then be re-started and other modules may then bestopped to determine other elements of the TM matrix. When a module isre-started, a start-stop timer can be restarted, and this initializationis performed for the next module after the start-stop timer expires.

In step 570, after all of the matrix elements of TM have beencalculated, the transfer matrix TM can be stored in a memory of theenvironmental maintenance system. The transfer matrix can be retrievedfor determining whether to change an operation level of an actuator.Such determination may be performed, for example, in methods 600-900.Certain embodiments for calculating matrix elements of a transfer matrixand a LOAD matrix are now described.

Calculation of a Matrix Element

In one embodiment with one operational parameter being changed at atime, the matrix elements of one column of TM that corresponds to thechanged operational parameter are determined after the second sensorvalues are received. If the operational parameter is P_(indx) (which hasa one-one correspondence with a module in this embodiment) and thesensor index is S_(indx), then a matrix element TM(S_(indx), P_(indx))can be computed as:

$\begin{matrix}{{{{TM}\left( {S_{indx},P_{indx}} \right)} = \frac{\left( {{Y\; 2} - {Y\; 1}} \right)}{({\Delta level})}},} & {{Eq}.\mspace{14mu} (1)}\end{matrix}$

where Y2 is the sensor value corresponding to S_(indx) after theoperational parameter P_(indx) is changed, Y1 is the sensor valuecorresponding to S_(indx) before the operational parameter P_(indx) ischanged, and Δlevel is a change in operation level of parameterP_(indx). A normalization factor may also be used, e.g., if the changewas not the same for each actuator. As described below, an energy factorcan be included, which could be considered a normalization factor.

When the sensor values are a temperature and the modules function tocool, values of TM will typically be negative, e.g., because shuttingoff a module (or other decrease) should make Y2 greater than Y1, and thechange in operation level (Δlevel) is negative. A similar result happenswith starting a module (or other increase) as the temperature differenceis negative, but Δlevel is positive. However, as mentioned above forstep 540, the counter result can occur, which is counterintuitive.

TM can be normalized such that all of the matrix elements can correspondto a same units of Δlevel. For example, regardless of the actual changein level used to calculate a particular matrix element (e.g., 10%, 10rpm), the matrix element can be multiplied by a factor so that everymatrix element will have the same value in the denominator. Thus, inlater steps a change in operation level can be used uniformly todetermine a change in predicted temperature as opposed to the change inoperation level being in different units for each matrix element.

In one embodiment, the Δlevel is a percentage of the change in theoperation level, e.g., 100% for turning on to maximum capacity of theoperation level, and −100% for turning off from the maximum operationlevel. In another embodiment, Δlevel is in units relative to minimumincrements used to create the transfer matrix TM. For example, if theincrement is 5V, 100 rpm, or other value (including percentage), then achange of 10V would be a value of 2 and 300 rpm would be a value of 3 ifthe transfer matrix TM was in units of the minimum increment. In anotherembodiment, if the transfer matrix was created in units based on amaximum level of operation across all modules (e.g. maximum power or fansetting), then Δlevel can be a fractional value. Each module can have adifferent range of operation level, e.g., one fan can have maximum speedof 2000 rpm and another 1000 rpm. In one aspect, Δlevel could providenormalization by itself. For instance, if the changes are always thesame for a particular parameter then a normalization factor may not beneeded.

In one embodiment, the operational parameter can be a percent capacity %Cap of heating/cooling flow that the module is operating. In thisembodiment, Δlevel can correspond to % Cap when the change is shuttingof the module. In one aspect, the value of % Cap can allow for anormalized measurement when all of the units are not operating at thesame capacity. % Cap is an example of a current operation level.

In various embodiments, % Cap is either returned from a query of theunit, or it is calculated as follows:

$\begin{matrix}{{{\% \mspace{11mu} {Cap}} = \frac{F_{P}\left( {{TR}_{P} - {TD}_{P}} \right)}{F_{D}\left( {{TR}_{D} - {TD}_{D}} \right)}},} & {{Eq}.\mspace{14mu} (2)}\end{matrix}$

where F_(P) is the flow rate of the stopped module before being stopped,TR_(P) is the return temperature of the respective module P before beingstopped, TD_(P) is the discharge temperature of the respective module Pbefore its operation level is changed, F_(D) is the design flow rate ofthe unit, and TR_(S)−TD_(D) is the design ΔT of the respective module P.

In one embodiment, the design ΔT may be the temperature difference whena cooling valve is all the way open or open to a preferable setting.Such value may depend on the temperature of the cooling substance (e.g.water) being used, which may be included as an additional factor. Inanother embodiment, modules with a fixed flow fan have the same valuesof F_(P) and F_(D). In such embodiment, the % Cap returned by a modulemay correspond to a setting of a cooling valve (e.g. valve 320).

In modules with a variable fan, F_(D) may be 100% of capacity or someother percent or value for which preferable (e.g. optimal) operation ofthe unit occurs. In one aspect, the value of F_(P) corresponds with asetting for the speed of the fan before the stopping. In otherembodiments, the heat (or cooling) flow rate FΔT (design or beforestopping) may be determined via other means, or simply just receivedfrom a module that measures this value.

Calculation of LOAD Matrix

In one embodiment, a LOAD matrix provides a measure of the effect ofdecreasing an operation level of a module on the capacity of the system.For example, the LOAD matrix can relate exactly how much the percent ofcapacity of a CRAC unit is increased to handle the heat load of serversof a computer room when one of the other CRAC units is turned off. Inone embodiment, the number of rows and columns of LOAD equals the numberof environmental maintenance modules.

The load matrix may be calculated at the same time as the transfermatrix TM. Thus, a column of TM could be calculated at a same time as acolumn of the LOAD matrix. In one embodiment, the load transfer functionmatrix (LOAD) is computed as follows:

$\begin{matrix}{{{{LOAD}\left( {C_{indx},K_{indx}} \right)} = \frac{\Delta \% \mspace{11mu} {Cap}_{{Cindx},{Kindx}}}{\% \mspace{11mu} {Cap}_{Kindx}}},} & {{Eq}.\mspace{14mu} (3)}\end{matrix}$

wherein Δ% Cap_(Cindx,Kindx) is the change in percent capacity of themodule C_(indx) induced by stopping (or otherwise decreasing) the moduleK_(indx), and wherein % Cap_(Kindx) is the percent capacity of themodule K_(indx) prior to stopping. The value of LOAD(C_(indx) C_(indx))equals −100% by definition. In one embodiment, the value ofLOAD(C_(indx), C_(indx)) is not calculated or may also be set to 0 (orother default value) as this value is typically not used. The LOADmatrix may be stored in a memory of an environmental maintenance system,and then used later for determining which modules to have an operationlevel increased or decreased.

III. Using TM to Reduce Energy Use

The transfer matrix can be used to keep the sensors within acceptableranges. The transfer matrix can also be used to determine operationlevels that keep the sensors within acceptable ranges while using areduced amount of energy. To determine the impact on energy, the changeof operation levels is assumed to be a fixed value for each actuator(although not all the same). In this way, each of the actuators can becompared to each other, and identify which actuator affects a sensor themost. Thus, if this sensor is out of range, the actuator with the mostimpact can be taken as the actuator that is the most energy efficient,since the amount of energy imparted to the actuator is the mostefficient.

In some embodiments, the amount of energy expended for an increase ofeach actuator is the same. For example, if each operational parameter ofan actuator is the power level of a module and each module has the sameenergy efficiency, then there are no energy efficiency differences.Energy efficiency equivalence can also be assumed when differences aresmall.

In other embodiments, the actuators have different energy consumption.In such situations the change in sensor values (Y2−Y1) can be modulatedby an energy factor. The modulated results can be compared so thatenergy consumption is accounted for in determining which actuators tochange. For example, an actuator that uses less energy for a givenchange would have the modulated result increased relative to thedifference in sensor values, thereby increasing the preference forhaving that actuator be changed. Whereas, an actuator that is lessenergy efficient would have the difference in sensor values reducedrelatively. Such modulation for energy consumption can be included intothe transfer matrix itself. The value of the modulation can bedetermined by changing each actuator by a same percentage and recordingthe energy usage. In various embodiments, the modulation can includemultiplication, division, addition, and as an additional point in acoordinate system, which could involve addition, multiplication, andadditional functional operations. Instead of a modulation, someembodiments can use an energy consumption value as an additional factorin determining which actuator to change. For example, the actuator thatprovides a suitable change in sensor values while having the smallestenergy consumption can be chosen.

In one embodiment, a module's efficiency for heating/cooling flow is anexample of an energy consumption factor. The efficiency may be taken ascertain input settings of an actuator of a module (e.g. chilled watervalve setting) or as the percent capacity from Eq. 2. In anotherembodiment, an efficiency η of a module C_(indx) is computed as follows:

$\begin{matrix}{{{\eta ({Cindx})} = \frac{\% \mspace{11mu} {Cap}}{FanSpd}},} & {{Eq}.\mspace{14mu} (5)}\end{matrix}$

where FanSpd is the percent of full fan speed that the module iscurrently using. In one embodiment, the fan speed is 100% for modulesthat do not have a variable fan. For modules with a variable fan, thefan may be operating at less that the maximum setting, and thus at below100%.

In one aspect, using the fan speed in the denominator can place apreference on stopping modules that do not have variable fan speedsbecause fan speed will be 100% in that case, and the efficiency will beless. As shown, a less efficient module has a lower efficiency since theamount of cooling capacity is less for a given fan speed. Otherefficiencies can include any percent output divided by a level of input,thereby measuring efficiency. For example a cooling output for aspecific chilled water valve setting can be used to compute anefficiency for the actuator of the valve.

IV. Maintaining Sensor Values in Range

FIG. 6 is a flow diagram illustrating a method 600 of controlling anenvironmental maintenance system to maintain sensor values within adesired range with high efficiency according to an embodiment of thepresent invention. Method 600 determines which one or more actuators arethe best for changing (increasing or decreasing) operation levels when aparticular sensor value has a sensor value outside of the desired range.For example, if the temperature of a sensor (e.g. a cold aisle sensorthat is too hot) is beyond a threshold, method 600 can determine whichmodules should have an operation level increased (e.g., started) tobring the sensor back in range as quickly as possible or in an energyefficient manner. In one embodiment, the method 600 is performed inwhole or in part by controller 15, or another computer or processordescribed herein.

In step 610, a sensor (e.g. one of sensors 3) whose sensor value isoutside of the desired range is identified (e.g., a temperature is abovea threshold value). In one embodiment, an application (e.g. softwarerunning on a processor of the system) can periodically check if there isa sensor value out of range. For systems that are cooling a room, such asensor can be referred to as a hot spot since the sensor value is hotterthan desired. For example, a sensor that is too hot may be identified bymonitoring the sensors and having an alarm signal be sent when a sensorbecomes out of range, e.g., higher than a threshold. The alarm signalmay be generated internal to controller 15 or at another part of acontrol system.

In some embodiments, the desired range can be defined by a target valuefor a room. Examples of ranges include plus or minus a certain valuefrom the target value, any value below the target value, or any valueabove the target value. The desired range may be web-configurable, witha default value (e.g. 83 degrees Fahrenheit for temperature of a datacenter). In another embodiment, a sensor may be identified as being toocold, e.g., when the environment is required to be above a particulartemperature. In such an embodiment, the modules would be providingheating and not cooling.

In step 620, one or more actuators whose operation level can beincreased are identified as increasable actuators. The operation levelcan refer to any operational parameter for an actuator of a module.Examples of when an operation level may not be increased include when anactuator is at or a near a maximum operation level. In one embodiment,the criteria for this determination can be if the operation level iswithin a predetermined amount (e.g. a percentage) from a maximum level.In some instances, only some of the operational parameters of a specificmodule can be increased, while in others all of the operationalparameters may be increased. In some embodiments the increase can berestricted to modules that are stopped, thus the increase would be astart command.

In some embodiments, decreasing an actuator may actually cause a sensorto move within range, or at least closer to within range. Such instancesare described above for step 540 of method 500, e.g., when transfermatrix elements have an opposite sign. In such embodiments, step 620 canbe modified to also include the identification of actuators whosedecrease in operation level can provide a beneficial change in theidentified sensor value. Below reference is made to increasing anoperation level, but decreasing an operation level may also beperformed.

In step 630, the system predicts amount (change value) that anincreasable actuator (i.e. identified in step 620) would change thesensor value that is out of range. This prediction can be done for eachincreasable actuator. The predicted change value can be estimated byusing a predetermined value (e.g. 50% or 100%) for an amount that theoperation level of an actuator would be increased. In one embodiment,the predicted change value predicts an extent that starting therespective stopped module would change the temperature of the sensor isdetermined. Thus, in an embodiment, method 600 can estimate the impacton extinguishing a hot spot by starting each stopped CRAC unit.

In some embodiments, the predetermined increase in the operation levelfor each actuator is the same for purposes of determining the predictedchange value. In other embodiments, the predetermined increase candiffer among the increasable actuators. For example, the increase can bea certain percentage (e.g. 10%, 30%, or 100%) of the increase in theoperation level. The actual amount of increase actually implemented candiffer from the predetermined increase used to determine the predictedchange values. In one embodiment, the predetermined increase is a fullamount that the operation level of the actuator (which may be equivalentto the module) can be increased. For example, as different modules maybe operating at different levels before the change, each module can havea different increase. Step 620 can account for the predeterminedincrease and/or actual increase to ensure that the identified actuatorscan actually have their operational levels increased by an appropriateamount.

In one embodiment, the predicted change value AY is obtained using thetransfer matrix determined, e.g., as described above. One embodimentuses

Y _(post) −Y _(pre) =TM(S _(indx) ,P _(indx))*Δlevel(P _(indx))  Eq.(6),

where Y_(post) is the estimated sensor value after a change, Y_(pre) isthe current sensor value that is out of range, S_(indx) corresponds tothe sensor that is out of range, and P_(indx) corresponds to an actuatorbeing considered for increasing an operational level. The predeterminedincrease is Δlevel, which may be different than the value used to createthe transfer matrix TM. And, as mentioned above, Δlevel may be differentthan an actual amount that the actuator is increased.

Accordingly, in some embodiments, Y_(post) can be the estimated hot spottemperature after starting CRAC P_(indx), Y_(pre) can be the hot spottemperature, S_(indx) can correspond to the sensor having the hot spottemperature, and P_(indx) can correspond to a CRAC being considered forstarting. In one embodiment, Δlevel(P_(indx)) is the estimated change incapacity resulting from starting a module.

Referring back to FIG. 6, in step 640, an actuator is selected forincreasing based on the predicted change values. In one embodiment, thevalue of Y_(post) is considered the predicted change value. In anotherembodiment, the value of Y_(post)-Y_(pre) is the predicted change value.Other predicted change values using TM may also be used. The changevalues can be used to ensure that the sensor value will be broughtwithin range. In one aspect, Y_(post) may be chosen to be lower/higherthan the maximum/minimum value defining the range by a specified amount.

For example, Y_(post) or Y_(post)-Y_(pre) can be used to determine whichactuators can change the sensor value to be within range. The changevalues can also determine which actuator has the biggest change invalues for the sensor S_(indx). In one embodiment, the module with thelargest predicted change value is used because this module willpresumably cure the out of range condition with the least amount ofoperational change, and thus the least amount of energy. In anotherembodiment, the module with the largest predicted change value can alsobe assumed change the sensor value the fastest, and naturally change thevalue the most so that another out of range condition is less likely forsensor S_(indx). For example, the CRAC unit that provides lowestY_(post) may be used. The change value may be a positive or a negativevalue. Thus, the term largest may refer to the smaller number if thevalue is negative. In another embodiment, any one of the units that havea predicted change value that is greater than a change threshold may beused.

As mentioned above, the transfer matrix can include energy consumptionfactors for each of the actuators, e.g., as described above for Eq. 4.These energy consumption factors can also be used to modify the changevalues, e.g., if the factors are not in the transfer matrix already. Forexample, a module may be selected based on a minimization of fan powerconsumption or other power while still having Y_(post) to be withinrange. In one embodiment, there is a preference for starting a modulethat has a variable fan speed, as these modules can operate below amaximum capacity.

In step 650, the operation level of the selected actuator is increased,or possibly decreased as mentioned above. As mentioned above, in oneembodiment, the application shall increase the operation level of theactuator that has the biggest impact on extinguishing the hot spot (e.g.starting the CRAC unit that produces the lowest estimated temperature atthe hot spot). More than one actuator or module can be increased if theestimated Y_(post) with the actual change Δlevel(P_(indx)) is below atarget value. In one embodiment, if none of the Y_(post) values exceed atarget value (or minus a deadband), then two actuators may be increasedat the same time. The deadband can ensure that a sufficient changebeyond an edge of the desired range is achieved.

As mentioned above, the operational parameter whose level is beingincreased can be an output parameter, e.g., the percent capacitymentioned above. A problem of using an output level can be that one maynot be able to predict exactly what the output level is for a giveninput, particularly given that the output level may depend on theoperation of other modules and actuators. Accordingly, it can bedifficult to predict the exact change in operation level that will beachieved. In some embodiments, the change in operation level isestimated from the existing operation levels.

Some embodiments can estimate how that cold air is redistributed afterthe increase. A uniform redistribution can result in the default valueof the average output levels of the operating modules times N/(N+1)where N is the number of operating units before increasing the newmodule for the actual output level. The average may be obtained fromeach module, or be assumed to be the same for all modules, and thus onlyone output level may be determined. In another embodiment, the outputlevel may be determined from the LOAD matrix described above (equation3), or a similar LOAD matrix that is created by increasing a module andmeasuring the changed capacity. The actual capacity may be differ fromthe actual capacity, but this estimated value can help determine if morethan one module needs to be increased.

In step 660, other actuators are prevented from being increased, e.g.,for a certain period of time or based on a criteria (e.g. a quasi-steadystate condition as described above for method 500). In one embodiment, atimer is started after the selected one or more actuators are increased.In one aspect, the timer is a web-configurable timer (default 15minutes) that shall prevent another increase until the timer expires. Inanother embodiment, a module can be prevented from increasing until thesensors values have reached an equilibrium in response to increasing anactuator. In one aspect, this prevents too many actuators fromincreasing at similar times, and thus using more units than arerequired, which might use too much energy.

In step 670, the transfer function matrix TM is updated. For example,the values of TM for the increased actuator (e.g. a started module) maybe updated using equation 1. In this manner, one can determine howaccurate the initialization was or adapt to changes in the load whosetemperature is being maintained, and TM can be refined in response.Accordingly, this updating can handle a changing relationship in thetransfer matrix. In this way, the system would change along withchanging variables of the system, and thus may continue to provideaccurate estimations.

In some embodiments, the first step of the update can be to recordsensor values before any operation level is increased, as well as theoperation level (e.g. percent capacity) of the selected actuators (whichcan include identifying the actuator to be off). A next step of theupdate can be to record the sensor values after a set time period orafter the criteria is met, as well as the operation level of theactuators that have been increased. In one embodiment, the new matrixelements of TM in Equation 1 is calculated for the column(s) jcorresponding to the actuators that are changed. The new TM is thenupdated as follows:

TM(i,j)_(new) =g*TM(i,j)_(new)+(1−g)*TM(i,j)_(old)  Eq. 7,

where g is between 0 and 1 (e.g. a default 0.3). In one embodiment, thevalue of g could vary with time or depend on another variable. In otherembodiments, other older TM matrices (i.e. matrix elements from previousupdates, such TM_(older)) may be used to mix to obtain the TM_(new).

In one embodiment, the operation levels of each of the actuators aremeasured and each of the columns are updated. Thus each of the rowswould have the same change in sensor values, but the change in operationlevels would vary. These other matrix elements can be computed when theoperation level is an output level, which may change even though theinput to only one actuator is changed.

In other embodiments, an aisle sensor (or other sensor) that is too coldmay also be used to identify a cold spot. The above method may be usedto turn on an HVAC unit that provides heating, e.g., when the system isattempting to heat an environment relative to an ambient temperatureinstead of cooling it as described above. In embodiments where thesystem is to be cooled, the sensing of a cold spot may trigger astopping of one of the HVAC units. Such preventing of cold spots canhelp as low temperatures have been shown to be associated with prematuredisk drive failures. The stopping of a module may occur for otherreasons as well.

Method 600 may repeat. For example, a check may be performedperiodically to determine if any sensor is out of range. In oneembodiment, the amount of increase can be at least a predeterminedamount (which may be less than 100%). If the increase is less than full,on the next round, the same one or more actuators can be chosen.

In some embodiments, a preference may be made for starting or stoppingan actuator (potentially a whole module) as opposed to just increasingor decreasing by an intermediate value. In one embodiment, if turning onan actuator does not bring the sensor value back in range then otheractuators that are currently running may be analyzed. In anotherembodiment, the preference is only performed when there is a mix of thatcan only be turned on or off, while the other actuators have otherintermediate settings. These embodiments can be applied to othermentioned described herein. Two different transfer matrices can be used:one for determining whether to start or stop; and the other fordetermining whether to do a variable increase or decrease, which may beless than 100%.

Selecting Parameter to Change Using Randomness

If the operational parameter (e.g. power to a module) that provides thelargest change value is always chosen, then certain parameters willalways be changed. For example, changing the same actuator often maycause that transfer matrix to incorrectly weight that actuator, and thuscause a selection of that same actuator more in the future. To removethe bias, some embodiments select another actuator at random. Theselection may still be restricted to actuators that still bring thesensor value within range. The randomness can prevent any particularpatterns in the increasing of actuators, which would reflect biases andnot a natural function of the system.

In one embodiment, the selection randomly chooses to a second optimalactuator. The total percentage that the sub-optimal actuator is chosencan be selected (e.g. 20% of the time), but the exact times for thesub-optimal selection may be random. In another embodiment, eachactuator that is predicted to bring the sensor value back in range isallowed to be picked during a random selection.

Energy Savings Vs. Reliability

As mentioned above, sometimes decreasing an actuator can bring about adesired change in an out of range sensor value. Sometimes the change maynot be sufficient to cause the sensor value to be back in range, but thechange is still in the desired direction. For example, in cooling a datacenter, stopping a module can actually cause a temperature of a sensorto decrease.

In some embodiments, it is more desirable to save energy, than to havethe sensor values back in range as quickly as possible. Thus, there canbe a preference for decreasing an actuator than for increasing anactuator. In one embodiment, such a preference can be made among allactuator changes that can bring the sensor back in range. In anotherembodiment, such a preference can be made for a decrease even if thechange does not bring the sensor back in range, as long as the change istoward the desired range. For example, if the range is less than 83° andthe hot spot temperature is 87°, then a predicted change of an actuatorto change the temperature to 85° would be acceptable for choosing todecrease the actuator. In one embodiment, the decrease is alwaysstopping the actuator.

V. Saving Energy by Decreasing an Operation Level

When all of the sensors are within range, operation of the actuators canbe decreased to save energy. Such decreased operation can be controlledto prevent an out-of-range condition for the sensor values. For example,as predicted change values were used above to determine which actuatorswill bring sensor values back into range, predicted change values can beused to determine which actuators will not cause an out of rangecondition.

FIG. 7 is a flow diagram illustrating a method 700 of controlling anenvironmental maintenance system by decreasing operation of actuatorsaccording to an embodiment of the present invention. Method 700determines which actuators are acceptable to decrease. In oneembodiment, the method 700 and other methods mentioned herein areperformed wholly or partially by controller 15, or another processordescribed herein.

In step 710, actuators that are currently using energy (i.e. running)are identified. In various embodiments, the energy use may be electrical(e.g. power to a fan), thermal such as providing heating/cooling (e.g.supplying cold water to a cooling element), or combustible (e.g. burninggas to provide heat). In one embodiment, the identified actuators arealso limited to the actuators that are available for decreasing. Forexample, if the power to a module is only operational parameter to bedecreased, the module is viewed as a single actuator.

In step 720, the system estimates the resulting sensor values if anoperation level of a running module were decreased by at least apredetermined amount (e.g. 50% or 100%). Resulting sensor values can bedetermined for each running module. The operation level corresponds toan actuator of a module, which can be considered the module itself Asthere can be more than one actuator for a module, resulting sensorvalues can be determined for a predetermined amount of change for eachactuator. In one embodiment, the following equation is used to determinethe change in sensor value for a predetermined change Δlevel forparameter

P _(indx) :Y _(post) =Y _(pre)+TM(S _(indx) ,P _(indx))*Δlevel(P_(indx))  Eq. 8.

In step 730, a first set of one or more of the plurality of the modulescurrently running that have none of the estimated sensor values outsideof a first range is determined. For example, in one embodiment, ifturning off a module will not cause an out-of-range condition, then thatmodule would be part of the first set. In another embodiment, ifdecreasing one or more actuators of a module would not cause anout-of-range condition, then hat module would be part of the first set.As described herein, each sensor can have a different range, and theterm first range encompasses these different ranges. The range caninclude thresholds and a deadband value as described herein.

In step 740, an operation level of at least one module of the first setis decreased in response to the determination that one or more of theplurality of the modules currently running have none of the estimatedsensor values outside of the first range. In one embodiment, theoperation level may be an operation level for the whole module, e.g.,turning off the module. In another embodiment, more than one operationlevel of an actuator may be decreased for a module. In yet anotherembodiment, various actuators for multiple modules may be decreased. Inan embodiment, the combined effect of decreasing multiple actuators maybe achieved by assuming linearity and simply summing the changesresulting from the decreases.

In some embodiments, the first set of modules that might have anoperation level decreased is also restricted to modules that that havean efficiency (e.g. as computed from Eq. 5) less than a threshold (e.g.40%). In one embodiment, the actuator with the lowest efficiency isdecreased. In another embodiment, an operation level is not decreased ifthe load on the system after the decrease would be above a threshold. Inone implementation, the load can be calculated using the LOAD matrix ofEq. 3.

The estimated percent capacity % Cap of module C_(indx) of each runningmodule can be calculated as % Cap(C_(indx))=%Cap(C_(indx))+LOAD(C_(indx), K K_(indx))*% Cap(K_(indx)) Eq. 9, whereinthe load matrix provides a measure of the effect of decreasing anoperation level on the capacity of use of the other actuators. The loadmatrix element LOAD (C_(indx), K_(indx)) provides a measure of theeffect of stopping module K_(indx) on the capacity of module C_(indx).The estimated percent capacities can be summed or otherwise combined todetermine a total load.

% Cap(Sindx) is the CRAC unit that is going to be stopped and %Cap(Cindx) is for the CRAC unit whose efficiency is being determined.The overbar for % Cap(Cindx) denotes that the value is an estimate.

In one embodiment, decreasing the operation level of another module isprevented until a predetermined amount of time expires after decreasingthe at least one module of the first set. In another embodiment, thetransfer matrix elements can be updated in a similar manner as describedabove. For example, sensor values before and after the decrease can beused as well as the change in operation level of one or more actuators.

VI. Stopping a Module

As mentioned above, the process of identifying a module to decrease anoperation level of an operational parameter can result in stopping themodule completely. FIG. 8 is a flow diagram illustrating a method 800 ofcontrolling an environmental maintenance system by stopping modulesincluding a plurality of modules and sensors according to an embodimentof the present invention. Method 800 can determine which module is thebest one to stop.

Specifically, method 800 describes an example where the system canprovide cooling and the sensors are temperature sensors.

In step 810, a module whose efficiency is less than a threshold isidentified. In one embodiment, the threshold is web-configurable (e.g.default is 40%). The efficiency can be measured using Eq. 5 or usingother methods described herein. In one embodiment, method 800 can firstfind the module with the smallest value of efficiency on the firstiteration. In this manner, the unit that is doing the least amount ofcooling (or heating depending on the embodiment) will be targeted forpossibly shutting off. In other embodiments, more than one module may beidentified per iteration.

In step 820, the percent capacity of each module that would remain on ifthe identified module were shut off is estimated. In one embodiment, theapplication shall estimate the percent capacity of each CRAC unit thatwould remain on if the target unit were shut off using Eq. 9.

In step 830, an energy load is determined from the percent capacities.In one embodiment, the energy load is expressed as an average percentcapacity of the system. In another embodiment, the heat load is thetotal energy load of the system, e.g., as determined by summing terms ofthe percent capacities multiplied by the respective capacity of a unit.In another embodiment, the energy load corresponds to the largestpercent capacity of a module.

In step 840, it is determined whether the estimated energy load exceedsa load threshold. If the estimated energy load does not exceed the loadthreshold, then the method proceeds. If the estimated energy load doesexceed the load threshold, then the method returns to step 810 toidentify another module for possibly stopping. This determination helpsto prevent the system form being overloaded by the stopping of a module.

In one example, if shutting off the target module would not cause theenergy load to exceed a target percent of the capacity that would remainon after a unit is shut off (default=90%), then that module is shut offIn one embodiment, if shutting off the least efficient module wouldoverload the modules that remain on or cause an out-of-range condition(e.g. a hot spot), then the next lowest efficient module shall beevaluated for stopping.

In an embodiment where the energy load is the largest percent capacityof a module, the efficiency threshold may be larger than that used forthe total capacity (e.g. 95%). Both types of thresholds may also beused.

In step 850, the sensor temperatures if the identified module werestopped are estimated. In one embodiment, the application estimates thecold aisle temperatures if the target CRAC unit were shut off using Eq.8.

In step 860, it is determined whether any of the estimated sensor valuesexceed a threshold, i.e. are outside of a range. This step helps toprevent creating a hotspot. If the estimated sensor values do not exceedthe threshold, then the method proceeds. If the estimated sensor valuesdo exceed the threshold, then the method returns to step 810 to identifyanother module.

In one example, if shutting off the target module would not cause anysensor values to exceed the threshold minus a deadband (e.g. 83 degreesF. minus 2 degrees F.), then the target module can be stopped. The useof the deadband can ensure that the sensor will not get close to thethreshold.

In one embodiment, the target temperature (or other sensor value) usedto determine a hot spot is the same target temperature used to determinewhether a sensor temperature exceeds a target threshold minus adeadband.

In step 870, the identified module is stopped. In one embodiment, afterstopping the identified module, a start-stop timer, e.g., with aweb-configurable limit (default 15 minutes) shall be started, andanother CRAC unit shall not be stopped until the start-stop timerexpires.

Also, the values of TM corresponding to the target CRAC unit may beupdated as described above after the start-stop timer expires. In oneaspect, the first step of the update is to record the cold aisletemperatures and percent capacities of the CRAC units that are on,including the one being stopped, before the start-stop timer isrestarted. The second step of the update is to record the cold aisletemperatures and percent capacities after the start-stop timer expires.The values of TM in Equations 1 and 2 are then computed and updated,e.g., according to Equation 5.

VII. Starting and Stopping

In some embodiments, a control system can keep track of which actuatorsshould be changed (increase or decrease) to efficiently maintain sensorvalues within the desired range, and at different times track whichactuators can be decreased to save energy without causing an out ofrange condition. In one embodiment, the logic for maintaining sensorvalues within range trumps the logic for decreasing energy use. Forexample, if there is a CRAC with a low efficiency and a there is a hotspot at the same time, then a CRAC will be started, not stopped.

FIG. 9 is a flow diagram illustrating a method 900 of controlling anenvironmental maintenance system by increasing or decreasing operationlevels of modules to maintain sensor values within a desired range andreduce energy use according to an embodiment of the present invention.Method 900 can determine which actuator is best to increase or decreasebased on different conditions.

In step 910, the transfer matrix TM (see Eq. 1) and potentially the LOADmatrix (Eq. 3) are initialized. In one embodiment, the transfer matrixTM is initialized using method 500. In other embodiments, the transfermatrix TM may be received by a control system when default values areassumed or when initialization is performed by another control system.

In step 920, it is determined whether a change in an operation level ofan actuator is prevented. As mentioned herein for various embodiments,the prevention may be determined by a timer or by criteria, e.g.,whether a quasi-steady state condition has been achieved in the sensorvalues. As an example, if the timer has not expired, then the processtakes the “yes” branch and waits until is acceptable to start or stop amodule, or other change an operation level of an actuator of a module.If the timer has expired then the process continues along the “no”branch.

The determination of prevention of a change can be made periodically ata relatively high frequency, such as every 10 or 30 seconds.

In step 930, the sensor values are monitored to determined whether anout-of-range condition is present. In one embodiment, temperatures (e.g.the cold aisle temperatures near the servers) are monitored to determinewhether a hot spot (or other violation of a threshold) is occurring. Ifan out-of-range condition is present, the process moves to step 940. Ifan out-of-range condition is not present, the process moves to step 960.

In one embodiment, the sensor values can be monitored even though achange in operation level is prevented. In this manner, once theprevention is lifted, the process can move forward with handling anout-of-range condition that has occurred when the prevention was inplace.

In step 940, a control system can determine which operationalparameter(s) to change to bring the sensor values back into range. Sucha determination can be made by any of the embodiments of method 600. Inone embodiment, the operational parameter is whether to start or stop amodule. In another embodiment, the operational parameter may be anoperation level of one or more actuators.

In step 950, a timer is started to prevent other operation levels frombeing changed until the timer expires and/or until a quasi-steady statecondition is achieved, as may also be done for other steps of othermethods mentioned herein. The TM and/or LOAD matrices may be updatedwhen the timer expires.

Returning to the branch if no out-of-range condition is present, in step960, it is determined whether any of the actuators (potentiallyincluding a whole module) have an efficiency that is below an efficiencythreshold. The efficiency may be determined by any of the methodsmentioned herein. In one embodiment, if no module is operating below theenergy threshold, then the process returns to step 920. In anotherembodiment, the process may continue even if no module is operating withan efficiency below the threshold.

In step 970, it is determined whether an actuator can have its operationlevel decreased (e.g. stopped) without causing an out-of-rangecondition. The prediction of whether an out-of-range condition willoccur can be performed as mentioned herein. For example, suchdetermination may be made by any of the embodiments of method 700. Inone embodiment, the module with the highest capacity that still does notcause an out-of-range condition is decreased (e.g. stopped).

In step 980, a timer is started to prevent other units from beingchanged until the timer expires and/or until a quasi-steady statecondition is achieved. The TM and/or LOAD matrices may be updated whenthe timer expires.

VIII. Calculation Multiple Columns of TM at Same Time

In one embodiment, the transfer matrix elements of one column at a timemay be calculated. For example, only one operational parameter (i.e.operation level of an actuator) may be varied, with the change in sensorvalues being used to updated a column of the transfer matrix TMcorresponding to the changed parameter. Such an embodiment allows one toisolate the interaction between an operation level and the sensorvalues. However, such a process can be slow as every actuator must bedecreased and then increased to obtain the matrix elements (Note thatthe TM may be updated after the decrease and the increase). To make theinitialization more efficient, some embodiments can change multipleoperation levels at the same time, and thus calculate matrix elementsfor multiple columns.

In some embodiments, multiple columns are determined at a time. In oneembodiment, each parameter is changed more than once, and an average(e.g. a weighted average) of a matrix element from each change is usedto determine a new matrix element. The process for a single operationalparameter can include turning off (or some other decrease) an actuator,calculating a matrix element, turning on the actuator, and againcalculating the matrix element, with an average of the two calculatedmatrix elements being determined. At each point of change of an actuatorin the above example, multiple actuators can be changed at the sametime. In some embodiments, the matrix elements are updated using arecursive least squares with covariance resetting to update the elementsof the transfer matrix.

In one embodiment, each element of the transfer matrix is thesteady-state change in a process variable (e.g., inlet air temperature)divided by a steady-state change in a control action, also called achange in operation level (e.g., starting and stopping a cooling unit).If the transfer matrix is arranged so that rows correspond to sensorvalues and columns correspond to control actions, then an element of thetransfer matrix is defined as follows:

$\begin{matrix}{{{{TM}\left( {i,j} \right)} = {\frac{{Y(i)}_{after} - {Y(i)}_{before}}{{u(j)}_{after} - {u(j)}_{before}} = \frac{{Y(i)}}{{u(j)}}}},} & {{Eq}.\mspace{14mu} (10)}\end{matrix}$

where Y is a vector of process outputs (e.g., server inlet airtemperature, pressure, humidity, etc) and where u is a vector of controlcommands, or potentially an output level. When the control commands areon/off, u takes values of 1 (on) or 0 (off).

In addition to the transfer matrix, an embodiment can use a covariancematrix. In one embodiment, the covariance matrix is a square matrix thesize of the number of control actions (i.e., it has the same number ofrows and columns as the number of elements of u). The initial covariancematrix can be an identity matrix multiplied by a large number (e.g.,1e6). In one aspect, the covariance matrix can describe the uncertaintyin the estimated values of the transfer matrix corresponding to thesensor. For example, the covariance matrix can provide the uncertaintyin the transfer matrix vector of parameters that corresponds to aparticular sensor. In an embodiment, changing the operation level of oneactuator more than another can reduce the elements of the covariancematrix corresponding to that actuator because there will be moreinformation about how that actuator affects sensors.

In one embodiment, initialization of the transfer matrix TM can beperformed according to the following method. Some of the following stepsmay be optional.

In step 1, a covariance matrix P is set to a diagonal matrix withdiagonal entries equal to 10⁶. In step 2, the transfer matrix values TMare set to zero. In step 3, all actuators (which may be equivalent to anentire module) are turned to 100% or some other common value. In step 4,the “before” temperatures are recorded. In step 5, a first actuator isturned down or off.

In step 6, the initialization waits until a configurable timer times out(e.g. with a default of 15 minutes), a quasi-steady state condition isreached, or a cold aisle temperature exceeds a limit (e.g. with adefault of 87 degrees F.). In step 7, the “after” temperatures arerecorded. In step 8, the temperature changes dY are computed.

In step 9, a learning update is performed. In one embodiment, a learningvector L is computed as L=P*du/(λ+du^(T)*P*du) (Eq. 11) and thecovariance matrix is updated using P=(I−L*du^(T))*P/λ (Eq. 12), where duis the vector of changes in the input control commands (or alternativelya change in an output level), and I is an identity matrix, and λ is aforgetting factor. In one aspect, λ can be “1” during initialization.The matrix can be made to be symmetric, e.g., by setting thebelow-diagonal elements to the above diagonal elements.

The transfer matrix can also be computed by computing prediction errorsand then updating the rows of TM, which may be done for all columns orjust the columns corresponding to the actuators that have been changed.In one embodiment, the error for sensor S_(indx) ise=dY(S_(indx))−TM(S_(indx),:)*du, and the new TM matrix elements areTM(sindx,:)=TM(sindx,:)+(L*e) across all columns or just the columns forthe actuators that have changed.

In step 10, the first actuator is turned back to the previous level, andthe second actuator is turned off or down. In step 11, a time is waited,e.g., as in step 6. In step 12, the “after” temperatures are recorded.In step 13, the temperature changes dY are computed. In step 14, alearning update is performed, e.g., as described above in Step 9. Instep 15, the next actuator is turned back to its previous level, and thenext actuator is turned down of off.

In step 16, the process can then go to step 11 for subsequent unitsuntil they have all been cycled up/down or on/off. The last actuator maybe cycled up/on by itself, just as the first actuator was initiallycycled down/off by itself. In step 17, the trace of the final covariancematrix can be stored as Tr_(final). In some embodiments, more than justone actuator is cycled up at a time, and more than one actuator iscycled down at a time.

A similar or same process can be implemented for updating the matrixelements while the system is controlling the environment. Such a processcan be performed when any change is performed on an actuator, e.g., asdescribed above for methods 500-900.

In step 101, it is determined which actuator(s) to change. In step 102,the “before” temperatures are recorded. In step 103, the operation levelof the actuator(s) is changed. In step 104, a time is waited, e.g., asin step 6 of the above method. In step 105, the “after” temperatures arerecorded. In step 106, the temperature changes (dY) are computed.

In step 107, the change in operation level (du) is computed. In step108, a learning update is performed, e.g., as described above in Step 9,where λ can equal 1.0. In step 109, the vector of prediction errors iscomputed as E=dY−TM*du. In step 110, the mean absolute prediction error|E|₁ and the maximum absolute prediction error |E|_(∞) are computed. Instep 111, the size of the prediction error as the weighted average |E|₁and |E|_(∞) is computed as

∥E∥=w*|E| ₁+(1−w)*|E| _(∞).

In step 112, a reset value for the trace of the covariance matrix isdetermined from an equation that links the size of prediction error tothe reset value of the trace. FIG. 10 provides an example of such anequation. In step 113, the trace can be updated by scaling each of theexisting values by a same multiplier such that the trace equals thereset value. In one embodiment, the covariance matrix is reset so thatits trace equals the trace reset value as follows:P=P*Tr_(reset)/trace(P). In step 114, the process repeats to step 101.

Any of the control systems, computers, or controllers may utilize anysuitable number of subsystems. Examples of such subsystems or componentsare shown in FIG. 11. The subsystems shown in FIG. 11 are interconnectedvia a system bus 1175. Additional subsystems such as a printer 1174,keyboard 1178, fixed disk 1179, monitor 1176, which is coupled todisplay adapter 1182, and others are shown. Peripherals and input/output(I/O) devices, which couple to I/O controller 1171, can be connected tothe computer system by any number of means known in the art, such asserial port 1177. For example, serial port 1177 or external interface1181 can be used to connect the computer apparatus to a wide areanetwork such as the Internet, a mouse input device, or a scanner. Theinterconnection via system bus allows the central processor 1173 tocommunicate with each subsystem and to control the execution ofinstructions from system memory 1172 or the fixed disk 1179, as well asthe exchange of information between subsystems. The system memory 1172and/or the fixed disk 1179 may embody a computer readable medium.

It should be apparent that various different modifications can be madeto embodiments without departing from the scope and spirit of thisdisclosure.

The specific details of the specific aspects of the present inventionmay be combined in any suitable manner without departing from the spiritand scope of embodiments of the invention. However, other embodiments ofthe invention may be directed to specific embodiments relating to eachindividual aspects, or specific combinations of these individualaspects.

It should be understood that the present invention as described abovecan be implemented in the form of control logic using computer softwarein a modular or integrated manner. Based on the disclosure and teachingsprovided herein, a person of ordinary skill in the art will know andappreciate other ways and/or methods to implement the present inventionusing hardware and a combination of hardware and software

Any of the software components or functions described in thisapplication, may be implemented as software code to be executed by aprocessor using any suitable computer language such as, for example,Java, C++ or Perl using, for example, conventional or object-orientedtechniques. Computer programs incorporating features of the presentinvention may be encoded on various computer readable media for storageand/or transmission; suitable media include magnetic disk or tape,optical storage media such as compact disk (CD) or DVD (digitalversatile disk), flash memory, and the like. The computer readablemedium may be any combination of such storage or transmission devices.

Such programs may also be encoded and transmitted using carrier signalsadapted for transmission via wired, optical, and/or wireless networksconforming to a variety of protocols, including the Internet. As such, acomputer readable medium according to an embodiment of the presentinvention may be created using a data signal encoded with such programs.Computer readable media encoded with the program code may be packagedwith a compatible device or provided separately from other devices(e.g., via Internet download). Any such computer readable medium mayreside on or within a single computer program product (e.g. a hard driveor an entire computer system), and may be present on or within differentcomputer program products within a system or network.

The above description of exemplary embodiments of the invention has beenpresented for the purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdescribed, and many modifications and variations are possible in lightof the teaching above. The embodiments were chosen and described inorder to best explain the principles of the invention and its practicalapplications to thereby enable others skilled in the art to best utilizethe invention in various embodiments and with various modifications asare suited to the particular use contemplated.

What is claimed is:
 1. A method of controlling an environmentalmaintenance system including a plurality of environmental maintenancemodules currently running and a plurality of sensors that measure avalue of a physical condition of an environment, the method comprising:for at least one of the plurality of the modules currently running:estimating sensor values of the sensors resulting if an operation levelof the module were decreased by at least a predetermined amount;determining a first set of one or more of the plurality of the modulescurrently running that have none of the estimated sensor values outsideof a first range; and decreasing an operation level of at least onemodule of the first set in response to the determination that one ormore of the plurality of the modules currently running have none of theestimated sensor values outside of the first range.
 2. The method ofclaim 1, wherein decreasing an operation level of at least one module ofthe first set includes stopping a module.
 3. The method of claim 1,wherein estimating sensor values of the sensors resulting if anoperation level of a first module were decreased by at least apredetermined amount includes: estimating resulting sensor values for achange in operation level of each of a plurality of actuatorscorresponding to the first module, and wherein decreasing an operationlevel corresponds to decreasing the operation level for the actuatorthat does not cause estimated sensor values to be outside of the firstrange.
 4. The method of claim 1 wherein the first range includes athreshold that is a combination of a target threshold minus a deadbandvalue.
 5. The method of claim 1, further comprising: identifying one ormore modules of the first set whose efficiency is less than anefficiency threshold; and for one of the identified running modules:estimating a percent capacity of each module that would remain on if theidentified module were shut off, the percent capacity being a measure ofthe percentage of the designed capacity at which the identified moduleis operating; determining a load from the percent capacities;determining whether the load does not exceed a first threshold;decreasing the operation level the identified module in response to adetermination that the load does not exceed the first threshold and noneof the estimated sensor values are outside of the first range.
 6. Themethod of claim 5, wherein the one of the identified modules is theidentified module with the lowest efficiency.
 7. The method of claim 5,wherein the load is determined from the percent capacity of each moduleand a design capacity of the module.
 8. The method of claim 5 whereinthe estimated percent capacity % Cap of module C_(indx) is %Cap(Cindx)=% Cap (Cindx)+LOAD(Cindx, Sindx)*% Cap(Sindx), for a loadmatrix LOAD, wherein the load matrix provides a measure of the effect ofstopping a module on the capacity of use of the remaining modules thatremain on, wherein the load matrix element LOAD (C_(indx), S_(indx))provides a measure of the effect of stopping module S_(indx) on thecapacity of module C_(indx).
 9. The method of claim 5, wherein theefficiency η for module C_(indx) is computed as the percent capacitydivided by the percentage of operation of a fan speed relative to amaximum fan speed setting.
 10. A computer program product comprising anon-transitory computer-readable medium storing a plurality ofinstructions that when executed cause a processor to perform a method ofcontrolling an environmental maintenance system that includes aplurality of environmental maintenance modules currently running and aplurality of sensors that measure a value of a physical condition of anenvironment, the method comprising: for at least one of the plurality ofthe modules currently running: estimating sensor values of the sensorsresulting if an operation level of the module were decreased by at leasta predetermined amount; determining a first set of one or more of theplurality of the modules currently running that have none of theestimated sensor values outside of a first range; and decreasing anoperation level of at least one module of the first set in response tothe determination that one or more of the plurality of the modulescurrently running have none of the estimated sensor values outside ofthe first range.
 11. The computer program product of claim 10, whereindecreasing an operation level of at least one module of the first setincludes stopping a module.
 12. The computer program product of claim10, wherein estimating sensor values of the sensors resulting if anoperation level of a first module were decreased by at least apredetermined amount includes: estimating resulting sensor values for achange in operation level of each of a plurality of actuatorscorresponding to the first module, and wherein decreasing an operationlevel corresponds to decreasing the operation level for the actuatorthat does not cause estimated sensor values to be outside of the firstrange.
 13. The computer program product of claim 10, wherein the firstrange includes a threshold that is a combination of a target thresholdminus a deadband value.
 14. The computer program product of claim 10,wherein the method further comprises: identifying one or more modules ofthe first set whose efficiency is less than an efficiency threshold; andfor one of the identified running modules: estimating a percent capacityof each module that would remain on if the identified module were shutoff, the percent capacity being a measure of the percentage of thedesigned capacity at which the identified module is operating;determining a load from the percent capacities; determining whether theload does not exceed a first threshold; decreasing the operation levelthe identified module in response to a determination that the load doesnot exceed the first threshold and none of the estimated sensor valuesare outside of the first range.
 15. The computer program product ofclaim 14, wherein the one of the identified modules is the identifiedmodule with the lowest efficiency.
 16. The computer program product ofclaim 14, wherein the load is determined from the percent capacity ofeach module and a design capacity of the module.
 17. The computerprogram product of claim 14 wherein the estimated percent capacity % Capof module C_(indx) is% Cap(Cindx)=% Cap(Cindx)+LOAD(Cindx,Sindx)*%Cap(Sindx)₅ for a loadmatrix LOAD, wherein the load matrix provides a measure of the effect ofstopping a module on the capacity of use of the remaining modules thatremain on, wherein the load matrix element LOAD (C_(indx), S_(indx))provides a measure of the effect of stopping module S_(indx) on thecapacity of module C_(indx).
 18. The computer program product of claim14, wherein the efficiency 77 for module C_(indx) is computed as thepercent capacity divided by the percentage of operation of a fan speedrelative to a maximum fan speed setting.
 19. An environmentalmaintenance system comprising: a plurality of environmental maintenancemodules; a supervisory controller communicatively linked to theenvironmental maintenance modules; a plurality of sensors that measure avalue of a physical condition of an environment and that arecommunicatively linked with the supervisory controller; a memorycomprising instructions which when executed cause the supervisorycontroller to: determine which environmental maintenance modules arecurrently running; for at least one of the plurality of the modulescurrently running: estimate sensor values of the sensors resulting if anoperation level of the module were decreased by at least a predeterminedamount; determine a first set of one or more of the plurality of themodules currently running that have none of the estimated sensor valuesoutside of a first range; and decrease an operation level of at leastone module of the first set in response to the determination that one ormore of the plurality of the modules currently running have none of theestimated sensor values outside of the first range.
 20. Theenvironmental maintenance system of claim 19, further comprisinginstructions that cause the supervisory controller to: identify one ormore modules of the first set whose efficiency is less than anefficiency threshold; and for one of the identified running modules:estimate a percent capacity of each module that would remain on if theidentified module were shut off, the percent capacity being a measure ofthe percentage of the designed capacity at which the identified moduleis operating; determine a load from the percent capacities; determinewhether the load does not exceed a first threshold; decrease theoperation level the identified module in response to a determinationthat the load does not exceed the first threshold and none of theestimated sensor values are outside of the first range; wherein theestimated percent capacity % Cap of module C_(indx) is% Cap(Cindx)=% Cap(Cindx)+LOAD(Cindx,Sindx)*% Cap(Sindx), for a loadmatrix LOAD, wherein the load matrix provides a measure of the effect ofstopping a module on the capacity of use of the remaining modules thatremain on, wherein the load matrix element LOAD (C_(indx), S_(indx))provides a measure of the effect of stopping module S_(indx) on thecapacity of module C_(indx).